In recent years, Evolved Universal Terrestrial Radio Access (E-UTRA) has been standardized by Third Generation Partnership Project (3GPP) as a communication specification for a radio device such as a mobile phone. For the E-UTRA, Single Carrier Frequency Division Multiple Access (SC-FDMA) method is supposed to be performed as a specification of a MODEM transmitting unit. This specification is specified in TS36.211 in the 3GPP documents.
For the SC-FDMA method, there are three types of physical channel to be transmitted. One is Physical Uplink Shared Channel (PUSCH), one is Physical Uplink Control Channel (PUCCH), and the other one is Physical Random Access Channel (PRACH). For the SC-FDMA method, there are two types of physical signal to be transmitted. One is Demodulation Reference Signal (DRS), and the other one is Sounding Reference Signal (SRS). For example, the SRS is used to check the quality of a transmission signal and to check how much the transmission signal is deteriorated on a propagation path between a radio device and a base station.
The radio device generates, for example, a Zadoff-Chu sequence to transmit the SRS, maps the generated Zadoff-Chu sequence in a frequency area, and converts the mapped frequency area into a signal of a time area by Inverse Fast Fourier Transform (IFFT) processing. The radio device copies the end of the signal subjected to the IFFT processing as a specified CyclicPrefix (CP) for the number of samples and then inserts the CP into the head of the signal subjected to the IFFT processing. Further, the radio device performs shift processing of ½ sub carrier frequency (for example, equivalent to 7.5 KHz) by multiplying the signal of the time area, which is subjected to the CP processing, by a twiddle factor, and generates the SRS by removing a high frequency of the signal subjected to the shift processing.
Japanese Laid-open Patent Publication No. 2011-40841 is an example of related art.